You've done nothing wrong and he is being unreasonable. Call him or leave a message if you can and tell him you can no longer sell the car due to having cancelled your loan due to him messing you about. He has no right to get shirty as he told you hedidn't want the car, and so you had to make alternate arrangements. If you still want to sell the car, don't drop the price or give him the full tank, and say that he's already put you out, and treated you like crap and that your not willing to alter any conditions of the sale.
I'd be tempted just to tell him to stuff it though. If he's been such a PITA, you'd be better off not dealing with him.